Power converters have been used in power supplies for voltage and power conversions. High efficiency power converters are needed in many applications to reduce the power losses and the heat generated, shrink the size and cut the cost of the power supplies and the cooling equipments. Power converters with wider voltage regulation range generally have lower power efficiencies compared to converters with narrower voltage regulation range and unregulated converters, and vice versa, given that other aspects and conditions of the converters are comparable. Voltage regulation capability and power conversion efficiency are often two conflicting things for high efficiency power conversions.